It is generally desirable for a fire-protection sprinkler head to deliver a fairly uniform spray pattern. In most sprinkler heads, the spray pattern is developed by directing a stream of water (or other fire-retardant liquid) from a throat (generally frustoconical in shape) against a deflector spaced a short distance from the throat. The deflector is generally supported at the region where two curved arms extending from the throat area meet. The arms do more than support the deflector; they generally support a strut member that holds a sealing button against the throat opening, and thus they are typically of substantial size. Their size as well as numerous other factors have an influence on the spray pattern.